1. Field of the Invention
The present invention relates to a device for delivering a pharmacologically active principle by electrolytic pumping.
Such a device is described, for example, in FR-A-2 195 461 which describes, in one of its embodiments, an electrolytic effect pump comprising a closed, variable volume first chamber containing a solid electrolyte (gelled electrolyte) giving off gas under the effect of a voltage applied to a pair of electrodes. The gas given off expands the first chamber which is generally bellows shaped.
The pump also includes a variable volume second chamber containing the active principle and opening out to the outside via an orifice enabling the principle to be dispensed. A rigid vessel defines the total volume of the two chambers, which total volume is constant, such that inflation of the bellows causes a reduction in the volume of the second chamber and corresponding, controlled expulsion of the active principle contained therein.
2. Description of the Prior Art
One of the main difficulties encountered with electrolytic effect pumps of this type is controlling the flow rate of the active principle.
The phenomenon of electrolysis is a process which naturally varies over time, given the gradual changes in the physico-chemical properties both of the electrolyte (in particular its own resistance) and of the electrodes (polarization).
The above-mentioned pump structure is unsuitable for obtaining a flow of active material which is simultaneously exact, accurate, and stable.
In addition, the pump structure proposed in that document is intended essentially for delivering the active principle continuously over relatively long periods of time. By using a solid electrolyte, the time constant of the electrolysis cell is relatively long because of the necessary diffusion through the gell. This electrolytic pump structure is therefore unsuitable for expelling very short spot doses, and a fortiori for expelling doses which are short and accurate.
New active principles such as growth hormone, releasing factor therefor, numerous peptides, hormones, chemical mediators, certain antibiotics, and certain antimitotics require discontinuous and frequent injections rather than continuous perfusion of substance at a rate which is fixed and constant over time, for the purpose of conserving their therapeutic effectiveness or for reducing side effects.
The flow rate characteristic of the injected active principle as a function of time must therefore have very narrow peaks which are impossible to achieve if the device has too long a time constant, as would be the case with a solid electrolyte.
In contrast, using a solid electrolyte solves the problem of permanent contact between electrodes and electrolyte since the gas given off by the phenomenon of electrolysis diffuses out from the gell and does not interpose itself between the electrodes and the electrolyte as could happen using a liquid electrolyte (particularly in the context of a device which is implanted or swallowed since at any given moment such a device may have arbitrary orientation in three dimensions).
The present invention seeks to remedy these drawbacks by proposing an electrolytic effect pump whose structure makes it possible to control the flow rate of the active principle extremely accurately, and also to make it highly constant over time.
Another object of the present invention is to propose a structure adapted to sequential injection of spot doses, i.e. doses which are short and accurate (typically for a duration of a few seconds or a few fractions of a second).
Another object of the invention is to provide a device which, by virtue of its specific configuration, is easily implantable or ingestable, so as to enable the active principle to be delivered in situ.